Optical position detecting method using asynchronous modulation of light source

Abstract

In an optical position detecting method, a light beam is intensity-modulated with a given periodic waveform, and is then emitted from an object light source. An image sensor captures an image of the light source and stores corresponding image data per pixel. Subsequently, the image sensor is accessed successively at least four times at a pitch which is less than 1/4 of that of the periodic waveform, so as to read the image data per pixel to form a time-sequential data. Subsequently, a scalar product computation of the time-sequential data is executed using a reference waveform which is asynchronous with the periodic waveform while having a period relatively close to the period of the periodic waveform, so as to derive first scalar data. Another scalar product computation of the time-sequential data is further executed using an orthogonal waveform which is out of phase by 90° relative to the reference waveform, so as to derive second scalar data. Finally, an image processing is performed using the first and second scalar data so as to extract a position of the light source.

What is claimed is: 
     
       1. An optical position detecting method which captures an image of a light source as an object by using an image sensor so as to measure a position of the light source, said method comprising: a light emitting step for emitting a light beam from said light source, said light beam being intensity-modulated by a given periodic waveform;   an image capturing step for receiving said light beam by the image sensor to capture said light source so as to store a corresponding image data pixel by pixel;   a reading step for accessing the image sensor successively at least four times at a pitch which is less than 1/4 of a period of said periodic waveform, so as to sequentially read the image data to form a time-sequential data;   a calculation step for executing a scalar product computation of said time-sequential data with a reference waveform which is asynchronous to said periodic waveform while having a period comparable to the period of said periodic waveform, so as to derive a first scalar data free of noise;   another calculation step for executing a scalar product computation of said time-sequential data with an orthogonal waveform which is out of phase by 90° relative to said reference waveform, so as to derive a second scalar data free of noise; and   a processing step for executing image processing according to said first and second scalar data derived pixel by pixel, so as to extract the position of said light source.   
     
     
       2. The optical position detecting method as set forth in claim 1, wherein said light emitting step modulates the period of said periodic waveform according to given additional information, and wherein an additional calculation step is further carried out for deriving phases of said periodic waveform at different sampling timings based on said first and second scalar data so as to derive the modulated period of said periodic waveform based on a time-variation of the phase of said periodic waveform to extract said additional information. 
     
     
       3. An optical position detecting apparatus which captures an image of a light source as an object so as to measure a position of the light source, said apparatus comprising: light emitting means disposed in the object for emitting a light beam from said light source, said light beam being intensity-modulated by a given periodic waveform;   an image sensor spaced apart from the object for receiving said light beam to capture said light source so as to store a corresponding image data pixel by pixel;   reading means for accessing the image sensor successively at least four times at a pitch which is less than 1/4 of a period of said periodic waveform, so as to sequentially read the image data to form a time-sequential data;   first calculation means for executing a scalar product computation of said time-sequential data with a reference waveform which is asynchronous to said periodic waveform while having a period comparable to the period of said periodic waveform, so as to derive a first scalar data free of noise;   second calculation means for executing a scalar product computation of said time-sequential data with an orthogonal waveform which is out of phase by 90° relative to said reference waveform, so as to derive a second scalar data free of noise; and   processing means for executing image processing according to said first and second scalar data derived pixel by pixel, so as to extract the position of said light source.   
     
     
       4. The optical position detecting apparatus as set forth in claim 3, wherein said light emitting means includes means for modulating the period of said periodic waveform according to given additional information, and wherein additional calculation means is further provided for deriving phases of said periodic waveform at different sampling timings based on said first and second scalar data so as to derive the modulated period of said periodic waveform based on a time-variation of the phase of said periodic waveform to extract said additional information.